This invention is directed towards testing underground formations in an oil well bore and is particularly useful for testing when a drill stem test is to be performed and it is desirable to be able to run tools through the drill stem and the tester to each areas in the drill string below the tester.
After an oil well has been encased and cemented, it usually becomes desirable to test the formations penetrated by the wellbore for possible production rates and general potential of the well. In doing so, a test string containing several different types of tools is utilized to determining the productivity of the well.
These tools might include a pressure recorder, a sample chamber, a closed-in-pressure tester, an hydraulic jar, one or more packers, a circulating valve, and possibly several other tools.
The testing procedure requires the opening of a section of the wellbore to atmospheric or reduced pressure. This is accomplished by lowering the test string into the hole on drill pipe with the tester valve and sample chamber closed to prevent entry of well fluid into the drill pipe. With the string in place in the formation, a packer below the tester is expanded to seal against the wellbore or casing to isolate the formation to be tested. Above the formation the hydrostatic pressure of the fluid in the wellbore is supported by the packer. The well fluid in the isolated formation area is allowed to flow into the drill string by opening the tester valve. Fluid is allowed to continue flowing from the formation to measure the ability of the formation to produce. The formation may then be closed in to measure the rate of pressure buildup. After the flow measurements and pressure buildup curves have been obtained, samples can be trapped and the test string removed from the well.
The difficulty with prior art testing devices is that they lack the ability to be openable and closable an indefinite number of times or else they fail to provide a fully open bore therethrough for full flow testing and the running of tools through the tester to the lower part of the drill string. In some areas, such as the North Sea, the cost of completing a well and testing are very high and it is extremely desirable to obtain the maximum amount of reservoir data from a single drill stem test.
The existing testers utilize flow passages through the walls, through annular spaces, or through restricted axial bores. Many can be opened and closed only one time. They require a "round trip" out of the hole and back into the hole with the tool string when it is desirable to run multiple flow and closed-in-pressure tests or when it is desirable to run a tool in the hole below the tester.
By the use of the present invention, it is not necessary to remove the test string from the well in order to run multiple flow and closed-in-pressure tests and the tester allows the running in of tools through the string to locations below the tester.
The advantages set out above are achieved in this invention by utilizing a full opening ball valve tool actuated by vertical reciprocation through a J-slot arrangement.
Other advantages embodied in the apparatus include an hydraulic metering system to regulate the opening time of the tester valve and a feature to bypass fluid trapped at hydrostatic pressure below the tester valve. The tester also incorporates a pressure balanced system to offset the natural buoyancy of the dry drill string in the drilling fluid and a shock absorbing system to prevent sudden applications of force on the valve mechanism thereby protecting it from damage and accelerated wear.